A General Accurate Current Limiting Strategy of Grid-Forming Converters Based on Adaptive Virtual Impedance Regulated by Fuzzy Control

Grid-forming (GFM) converters are considered as a key solution for new power system with high penetration of renewable energy resources, owing to its voltage and frequency support ability. However, most of existing current limiting strategies of GFM converters are effective only in several predefined scenarios, and as a major solution, virtual-impedance-based methods fail to precisely restrict the current to a predefined value. Therefore, a general accurate current limiting strategy that functions in both islanded and grid-connected modes for various fault conditions is highly expected. In this paper, a current limiting strategy based on adaptive virtual impedance regulated by fuzzy control is proposed. This method shows excellent current limiting ability for various symmetrical and asymmetrical fault conditions in grid-connected and in islanded modes with the same predesigned parameters. Moreover, the proposed method accurately restricts the output current to the desired limit. The design of fuzzy controllers takes into account the feasible region of virtual impedance determined by small- and large-signal stability, thus ensures stable current limiting of the GFM converter. Finally, a series of experiments considering various fault scenarios are conducted to validate the universality and accuracy of the proposed current limiting strategy.